Waves

• Waves


  Oscillations of particles or oscillations of a field
• Waves


  • Can transfer energy
  • Can store energy
• Progressive wave


  Transfers energy
• Types of progressive waves

  • Longitudinal
  • Transverse
• Longitudinal wave


  Particles oscillate in the same direction as the energy transfer
• Transverse wave


  Particles oscillate at 90 degrees to the direction of energy transfer
• Displacement


  Positive or negative movement of a particle
• Amplitude


  Height of the wave
• Wavelength


  Distance from one wave to the equivalent point on the next wave
• Time period


  Time from one part of the wave to the equivalent part of the next wave
• Frequency


  Number of wave cycles per second
• Phase


  Part of the wave cycle that a point is in
• Examples of longitudinal waves

  • Sound waves
  • Ultrasound
• Examples of transverse waves

  • Electromagnetic spectrum
  • Waves on a string
  • Water ripples
• In a vacuum, electromagnetic waves travel at the speed of light (3.00 x 10^8 m/s)
• Speed of a wave


  C = f λ (speed = frequency x wavelength)
• Polarisation


  Transverse waves can be polarised, longitudinal waves cannot
• Polarisation is useful for sunglasses and radio/TV antennas
• Stationary wave


  Formed by the interference of a progressive wave and its reflection
• Node


  Position of no displacement in a stationary wave
• Anti-node

  Position of maximum displacement in a stationary wave
• Constructive interference


  Occurs when waves are in phase, resulting in a larger amplitude
• Destructive interference

  Occurs when waves are out of phase, resulting in a smaller amplitude
• Forming a stationary wave

  1. Progressive wave travels along

  2. Reflects off end

  3. Interferes with original wave
• Diffraction

  Spreading out of waves as they pass through an opening or through a prism
• Interference

  Interaction between two or more waves resulting in constructive or destructive effects
• Laser light is monochromatic and can be used to demonstrate interference patterns through a double slit
• Laser light


  Light amplification by the stimulated emission of radiation
• Laser light


  • Monochromatic - all the same wavelength
  • Coherent
• Wavelength of laser light

  Similar to the gap size for maximum diffraction
• Shining laser light through a double slit

  1. Diffraction pattern with maxima and minima

  2. Fringes of light
• Width of fringes (W)


  Equals lambda * D / s
• Reason for light and dark fringes is constructive and destructive interference
• Shining monochromatic light through a single slit

  1. Bright central maxima

  2. Dark points of destructive interference

  3. Bands of constructive and destructive interference
• Shining white light through a single slit


  1. Bright white central maxima

  2. Spectrum of colours spreading out on either side
• Diffraction grating

  Many closely spaced slits that create a diffraction pattern with bright spots
• Refraction

  Wave slowing down or speeding up as it passes from one medium to another, causing a change in direction
• Critical angle


  Angle of incidence where the angle of refraction is 90 degrees, causing total internal reflection
• Optical fibers


  • Use total internal reflection to transmit light signals
  • Have a core and cladding with a step change in refractive index
• Pulse broadening in optical fibers

  • Caused by material dispersion and modal dispersion